In my aforementioned patent, in which I have described in considerable detail an apparatus for coating labels with adhesive and applying them to objects such as bottles, I have pointed out that pre-existing systems for accomplishing a similar purpose operate with a stack of labels in a magazine adjacent a turntable provided with a plurality of pickup heads.
These heads are orbited about an axis spaced from the label magazine and are each first passed through a coating station at which a layer of adhesive is applied to the outer face of the pickup head. The pickup head is then pressed against the sheet of the stack at the discharge end of the magazine so as to pick up this sheet and transport it to a transfer element which takes the label off the pickup head and applies it to a container.
Prior to my development as described in that patent, there were two principal configurations in which the pickup head was made. In one such arrangement each pickup head had a face with a uniform radius of curvature centered on the rotation axis of the pickup turntable. This arrangement was disadvantageous in that it limited the number of labels which could be carried by the pickup arrangement at any given time since only a number of labels having a collective length equal to the circumference of the pickup device could be accommodated during each revolution of the device. In addition, when the faces of the pickup head were so formed, the turntable had to be rotated at a relatively low speed in order to insure that picked up labels were not dropped.
In any arrangement prior to my development as described in the patent, each pickup head had a radius curvature which was substantially smaller than the overall radius of the pickup device. The labels thus curled around the smaller pickup head to permit a large number of labels to be held on the pickup device at any one time. Even this arrangement had a disadvantage in that curling of the labels around each head was required and, when relatively stiff or inflexible labels were used, the labels could not be held adequately by the pickup device as it rotated. It was necessary further to rotate and drive each of these pickup heads separately, a face which resulted in increased vibration and were particularly disadvantageous when the labels are tightly curled since it further increases their tendency to fall off the pickup head.
Recognizing the disadvantages of such systems, in U.S. Pat. No. 3,923,589, I have described an improved system in which the rotatable turntable carries a plurality of pickup heads, each having a pickup face formed as a curved surface with a radius of curvature which varies over its length. This surface has, at one end, a radius of curvature which is centered on the axis of rotation of the head and has an increasing radius of curvature toward its other end, the pickup head being rotatably mounted at the first mentioned end. Each face had a rectified length (flat length), which was a least as long as the label to be picked up from a stationary magazine adjacent the pickup turntable.
While this device was highly advantageous and constituted a significant improvement over the art, in that it allowed the pickup surface of the head to roll without sliding on the end label of the magazine and was practically without sliding on the surface of the transfer drum, it still did not maximize the number of labels which could be carried by the pickup turntable or drum, especially for labels of considerable length.
The essential characteristic of the improved device which distinguished it from all other known constructions, resided in the configuration of the pickup head with its variable and known constant radius of curvature over the length of the pickup surface. At its smallest radius of curvature, the center of curvature coincided with the pivot axis of the pickup head, i.e. the distance between the axis of the pickup head and the first label of the magazine was equal to the smallest radius of curvature and the pickup surface of each pickup head met the label of the magazine at this smallest distance. The developed length of the pickup surface was at least equal to the length of the label and hence the pickup surface was practically cantilevered over the greater part of its length from the end at which it had the smallest radius of curvature.
To rigorously insure a rolling movement without slippage of the pickup head on the first label of the magazine, the directrix curve of the adhesion surface must correspond to the equation (in polar coordinates): ##EQU1## where: A is the shortest distance between the center of the rotating support and the first label;
R is the radial distance between the center of rotation of the respective pickup head and the center of the turntable or rotatable support carrying same; PA1 .theta. is the angle between the radius r and the starting radius, the latter being the smallest radius of curvature as measured to the center of the pivoting head and; PA1 r is the radius between predetermined point on the pickup face and the center of rotation of the respective pickup head carrying this face.
For a full explanation of this relationship see my prior patent identified above.
In the system described in that patent, however, the pickup head has an asymmetric configuration since the pickup surface extends only to one side of the region of minimum radius of curvature. The greatest part of the length of the pickup head corresponds to the portion with larger radius of curvature and thus the greater portion of the length of the label is carried to one side of the center of the pickup head. It is the rolling contact of this cantilevered portion of the pickup head, which must roll along the first label of the magazine which prevents detachment of the label and facilitates the removal thereof from the magazine.
Because of this asymmetrical configuration, the magazine is offset from an axial plane of the pickup drum and considerable stress is applied to the pickup head. Furthermore, since the greater part of the length of each label must be carried to only one side of each pickup head, the number of labels which can be accommodated on a given turntable and hence the number of pickup heads which can be provided is limited.